Technical Field
Embodiments of the invention relate generally to pulverized fuel power plants. Certain embodiments relate to systems and methods for increasing the concentration of pulverized fuel in a pre-ignition conduit of a pulverized fuel burner.
Discussion of Art
Pulverized fuel power plants have typically burned oil or natural gas to initially ignite the pulverized fuels, e.g., coal, that are to be combusted. As will be appreciated, this results in the consumption of large amounts of oil and gas. To reduce such consumption, plasma ignition systems have been developed to replace oil or gas ignition systems. More specifically, many plasma ignition systems use multi-stage, i.e., ‘stage-by-stage’ ignition technology to ignite pulverised fuels. In stage-by-stage systems, a relatively long pulverized fuel nozzle is employed that includes at least one and typically two or more ignition chambers located within the nozzle.
More specifically, in such systems, primary airflow containing pulverized fuel is ignited through the action of plasma generator to produce a plasma cloud in a first ignition chamber thereby generating a ‘first stage’ pulverized fuel flame. The first stage flame then ignites the pulverized fuel containing primary airflow in a second stage chamber, thereby forming a ‘second stage’ pulverized fuel flame. Finally, the ignited fuel enters into the furnace and reacts with oxygen in combustion air supplied through the burner, thereby forming a final stage flame.
Generally, the concentration of pulverized fuel in the ignition chambers is determined by a guide plate located in an elbow portion of a pulverized fuel nozzle. More specifically, the guide plate aligns the flow of pulverized fuel and primary air flow such that they are parallel to the plasma cloud. The guide plate also concentrates the pulverized fuel in proximity to a central axis of the burner and plasma cloud via a centrifugal separation effect. This, in turn, increases the concentration of the pulverized fuel entering the chamber, which facilitates ignition.
Due to space limitations within pulverized fuel nozzles, however, the pulverised fuel concentration in the chambers cannot easily be increased without affecting ignition behavior. As such, there is a need for a system and method for increasing the concentration of pulverized fuel that differs from those systems that are currently available.